There are many types of optical recording materials that are known. In many of the materials, the mode of operation requires that the unrecorded material have a high absorption and that the recorded areas, often referred to as pits, have high reflection. The high reflection pits are made by ablating away the high absorption recording material, usually exposing an underlying reflective support.
One of the currently popular forms of optical recordable element is the compact disc or CD. Digital information is stored in the form of low reflectivity marks or pits on an otherwise reflective background, the exact opposite of the above described optical recording materials. In this format, the optical information is most often in the form of read only memory or ROM. Optical information is not usually recorded in real time but rather is produced by press molding. In a typical process, the optical recording substrate is first press molded with a master containing the digital information to be reproduced. The thus formed information is then overcoated with a reflective layer and then with an optional protective layer. In those areas having the deformations or pits, the specular reflectivity is lower than in those areas not having the deformations.
It is desirable to produce optical recording elements which, when recorded in real time, produce a record that mimics the conventional CD on read out. In this manner, information can be added to the CD and the CD can be used on a conventional CD player.
One recently disclosed system of this type is the so called "Photo CD". In this system, conventional photographic film is first processed in a conventional manner. Then, the images from the film are digitized and the digital information is recorded in a CD readable form on an optical recording material. Images can then be played back on a conventional CD type player into a conventional television. Since a CD has a capacity for a number of digitized images that is greater than the typical roll of consumer film, it is anticipated that the user will want to add images and information to a partially recorded CD. Thus there exists the need for recordable, CD compatible optical recording material.
One method for forming a recordable element that mimics conventional mold pressed CD elements is to provide a transparent heat deformable support having thereon, in order, a layer of a dye that absorbs recording radiation and a reflective layer. Exposure of the recording layer through the support by the recording beam heats the recording layer to an extent that it is said that the surface of the heat-deformable support just adjacent to the recording-layer surface is deformed. Materials of this type are described in U.S. Pat. No. 4,940,618, European Patent Application 0353393 and Canadian Patent 2,005,520.
In the U.S. Patent and the European application mentioned above, the preferred dyes for the recording layer are indodicarbocyanine dyes. However, this type of dye does not have archival light stability and will in fact fade to an unusable state in only a few days of exposure to intense sunlight. These applications also disclose one phthalocyanine dye, that is a phthalocyanine dye that has a tert-butyl substituent in one of the .beta. positions on the aromatic rings of the dye. Similarly, the Canadian application mentioned above describes a large number of phthalocyanine dyes. However, all of these phthalocyanine dyes, while having excellent stability, are difficult and expensive to make. For a discussion of cyanine dyes, see Infrared Absorbing Dyes, edited by M. Matsuoka, Pages 19-33, Plenum Publishing Corporation, New York (1990)
For example, the phthalocyanine dyes of the Canadian application are made by first preparing components of the completed ring, which components have the necessary substituents, and then forming the phthalocyanine ring structure by thermally reacting the mixture with a metallic derivative and effecting ring closure. This is an expensive process characterized by low yield and difficult processes for separation of the desired dye from unreacted components. In a mass produced consumer product, cost of the recording layer dye is a major concern.